The area of testing the interface between the FCM and the ECM needs some work...yes, if you get to checking on steps 12 and 13, you must have the key on, engine running, FCM plugged in and be tapping into the wires. This is so hard to do, and such an uncommon failure, these steps should be absolutely the last things checked. There have been a few cases of ECM failures being the cause of loss of AC, but not very many. More common would be a wire broken.
But given your symptoms, I would check for a shorted or open coil winding in the AC clutch. That is the most common failure, and since the FCM sees the fault, it turns off the voltage, on SOME more modern FCMs.
So if your coil resistance is between 3 and 5 ohms (3.6 nominal) between the two wires feeding it, and the resistance from either wire to ground is greater than 100k ohm (usually shows the same reading as holding the probes apart in open air,,, 1+ or 1- on many modern meters), the the coil should be good.
The coil fails so often, and is so easy to check, that if your fans are working and the light is coming on, that is what you should check first.
Maybe this winter I'll get around to updating the PDFs??
